1. Field
Embodiments of the invention relate to electronic systems, and in particular, to radio frequency (RF) electronics.
2. Description of the Related Technology
Power amplifiers can be included in mobile devices to amplify a RF signal for transmission via an antenna. For example, in mobile devices having a time division multiple access (TDMA) architecture, such as those found in Global System for Mobile Communications (GSM), code division multiple access (CDMA), and wideband code division multiple access (W-CDMA) systems, a power amplifier can be used to amplify a RF signal having a relatively low power. It can be important to manage the amplification of a RF signal, as a desired transmit power level can depend on how far the user is away from a base station and/or the mobile environment. Power amplifiers can also be employed to aid in regulating the power level of the RF signal over time, so as to prevent signal interference from transmission during an assigned receive time slot.
The power consumption of a power amplifier can be an important consideration. One technique for reducing power consumption of a power amplifier is envelope tracking, which can involve varying the voltage level of the power supply node feeding a collector of a bipolar transistor of the power amplifier in relation to the envelope of the RF signal. However, such a power supply node can feed collectors of bipolar transistors that require a relatively large current. Thus, varying the power supply of the power amplifier in relation to the envelope of the RF signal can require a relatively large envelope tracking module, which can be relatively expensive and/or can consume relatively large amounts of power.
There is a need for improved power amplifiers. Furthermore, there is a need for power amplifiers having improved power efficiency.